An integrated assay for rapid detection of Escherichia coli O157:H7 on beef samples.

摘要

The Phast Swab is a vertically integrated assay for rapid detection of Escherichia coli O157:H7. A sampling device, an E. coli O157:H7 reporter bacteriophage carrying the lacZ gene, bacterial growth medium, E. coli O157:H7-specific immunomagnetic beads and a beta-galactosidase substrate (colorimetric or luminescent) are contained within a Snap ValveTM device. To conduct the assay, a sample to be tested is swabbed, and the swab is returned to the Snap Valve device; an 8-h enrichment follows. Any E. coli O157:H7 cells are isolated and concentrated by immunomagnetic separation, and the reporter bacteriophage is added to the test compartment, where it infects any viable E. coli O157:H7 present in the sample, forcing the bacteria to make large amounts of beta-galactosidase. Following the infection process (approx. 1 h), the cap of the Phast Swab is broken, releasing the substrate, which reacts with the beta-galactosidase to produce a colorimetric signal (read visually) or a luminescent signal (read with a hand-held luminometer). In this study, the Phast Swab was evaluated for its ability to detect E. coli O157:H7 on 100 cm2 portions of beef. The assay was capable of detecting 103 cfu/100 cm2 of E. coli O157:H7 within 12 h when a colorimetric substrate was used, and 101 cfu/100 cm2 within 10 h with the use of a luminescent substrate. The nature of this detection method is such that it effectively detects E. coli O157:H7 in a simple and rapid manner, with minimal need for instrumentation to interpret the test result.